If you shoot it and it works there are no necessary upgrades.
First mods? Mags. A sling or mount certainly. Optics? Maybe another discussion? AFTER YOU SHOOT IT A BIT Buttstock and pistol grip. Free float the barrel and install a better trigger. But shoot it a bit. Do what you like to do with the rifle and see where mods can improve your enjoyment with the rifle. I say enjoyment as for most of us purchasing rifles as civilians, it's all about how much we like shooting what we have, usually through the rifle doing well at what we own it to do. If your mods show an improvement in something you care about (group size, speed, comfort, etc), then they are worthwhile mods. If you have no idea why you have something on your rifle, it probably doesn't need to be there, yet, anyway.
I install a trigger (brand = guess) in every rifle I own or have to shoot on any regular basis. It doesn't matter what brand of rifle you have or how much you paid for it, the trigger is the interface between you and your rifle. It is the trigger that gives you your rifles feel and an SSA in a Norinco feels the same as an SSA in a more expensive rifle.
I am the testing horse at AEI, (why? because our weather sucks and no one else will do it). On my own I also like to shoot 300/600m targets. At work I sometimes have 40-50 uppers (usually less) to function test and zero. Doing that with a stock trigger, at this point, would make me want to punch myself in the face. My trigger hand, and my trigger finger, and it's little muscles... I would compare to a car seat. If you have ever spent 7+ hrs in a in a bad, no lumbar support seat, lets say an 88 Caravan, vs the same in an excellent, ergonomic seat, lets say a good Volvo (I hear). The way your back feels is the way my hand feels after a long session with a Geissele trigger vs a milspec type 5-8lb (hopefully) trigger. Sore and worn out vs relaxed and ready.
The trigger I use in my lowers is set up at a geometry that is easier to reach, and with a shorter reset required, and so is more comfortable to shoot every single time. The trigger also breaks exactly when my brain tells it to. The time from release to the shot occurring is faster than stock, so I haven't moved the rifle off my point of aim as much by the time the bullet leaves the barrel. The hammer hits the firing pin at the sweet spot, imparting less accuracy robbing vibration on my part. For me, this makes a difference. I have more confidence in my results shot for shot. I use less ammo to get the job done. I get to go back inside quicker.
For the same reasons, if I am shooting for accuracy, (and who isn't) I freefloat my barrels. In this way I trust that my own movements, bipod, rest, isn't deflecting the barrel and affecting the POI vs POA. It's isolating variables. I use a modular type forearm as I like the idea of installing rails where I actually want to mount something.
I'd also recommend the Magpul enhanced trigger guard as a worthwhile piece of comfort kit. It fills 'the gap' in front of the pistol grip. If you're not wearing gloves on your middle finger, that can get a bit raw otherwise.
Beyond the trigger, freefloat rail, sling, bipod, optic, buttstock, pistol grip and trigger guard, there is lots and lots of stuff on the market. My landlord loves his new green laser. It's your gun so whatever floats your boat. Have fun with it.
